Electroplating recovery process

ABSTRACT

Plating line passes parts from plating tank to insulated portion of dual chamber strike tank so as to cut drag out concentration by one half to further rinse tanks. Solution in certain rinse tanks passed through reverse osmosis cells and recycled to system. Most concentrated product of reverse osmosis cells placed in holding tank and concentrated therein by cycling through another reverse osmosis cell before periodic return to plating bath.

United States Patent Russell Dec. 23, 1975 [54] ELECTROPLATING RECOVERYPROCESS 3,658,470 4/1972 Zievers et a1. 204/232 Inventor: James P.Russell, Oregon y, 3,681,210 8/1972 Zlevers et al. 204/232 Oreg' PrimaryExaminer-T. M. Tufariello [73] Assignee: Winter Products (30., Portland,Attorney, Agent, or Firm-Klarquist, Sparkman,

Oreg. Campbell, Leigh, Hall & Whinston 22 F1 d: Se t. 6 19 1 p 74 57ABSTRACT [21] Appl' N03 503631 Plating line passes parts from platingtank to insulated portion of dual chamber strike tank so as to cut drag[52] US. Cl 204/14 R; 204/232; 204/237 out concentration by one half tofurther rinse tanks. [51] Int. Cl. C07B 5/00; A44B 9/12 Solution incertain rin tanks p d hrough reverse [58] Field of Search 204/14 R, 232,237-241, osmosis cells and recycled to y Most concen- 204/267 269 tratedproduct of reverse osmosis cells placed in holding tank and concentratedtherein by cycling through [56] References Cit d another reverse osmosiscell before periodic return to UNlTED STATES PATENTS Platmg bath-$637,467 1/1972 Spatz 204/14 R 8 Claim 3 Drawing Figures U.S. PatentDec. 23, 1975 Sheet 2 of2 3,928,146

PDOU EO ELECTROPLATING RECOVERY PROCESS BACKGROUND OF THE INVENTIONRealization of the injury to rivers, lakes and oceans by reason of thedischarge therein of heavy metal solutions and other chemicals hascaused severe restric tions, both voluntary and legislative, upon thedischarge of such materials into such bodies. Moreover, the increasingcost of chemicals and metals has increased the necessity of theireconomical use. i

Electroplating solutions have presented particular problems indisposaland efforts have been directed to recovering the chemicalsutilized therein. US. Pat. No. 3,637,467, for example, described aprocess utilizing a reverse osmosis unit in connection with the recoveryand recycling of chemicals in a gold plating operation. The system,therein described would not be suitable for a brass or similar largevolume flow rate plating operation. Other systems utilizing reverseosmosis units have been suggested, but none, so far as is known, havebeen capable of continuous plating operation while eliminating totallyany discharge outside of the system.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide an improved completely closed system for recoveryof chemicals and water in an electroplating system.

Another object is to provide a closed recovery system that will permitcontinuous plating operation.

In accordance with the invention parts to be plated are, followingsuitable preparation, subjected to a strike plate in a dual chambertank, one chamber of which constitutes an electroplating bath, the othera drag out or pre-rinse bath although the two portions are in fluidcommunication. Following the strike, the parts are placed in aconventional plating bath. After plating they are dipped in thepre-rinse portion of the dual chamber tank and thereafter passed througha series of rinsetahks substantially ro remove all plating chemicalsfrom the parts. The solution in the dual chamber tank is one half theconcentration in the plating tank thereby reducing by one half theamount of chemicals carried over into the rinse tanks.

Solution in various of the rinse tanks is treated by reverse osmosis toremove chemicals, some solution being returned to other of the rinsetanks. The concentrate from treatment of the solution in the first rinseis placed in a holding tank. This solution is itself passed through areverse osmosis unit, the permeate being returned to a rinse tank, theconcentrate to the holding tank. Periodically the contents of theholding tank are returned to the plating bath.

Other objects and advantages of the invention will become apparenthereinafter.

- DRAWINGS 8 FIG. 1 is a schematic flow chart showing the path ofobjects to be electroplated in accordance with the invention';

FIG. 2 is a semi-schematic cross sectional view of a dual chamber tankutilized in the system of the invention; and j FIG. 3 is a schematicflow chart of the process of the invention indicating thereon theoperating conditions at one period of the process.

DETAILED DESCRIPTION OF THE INVENTION The illustrated embodiment of theinvention. is for plating brass upon articles such as furniture hardwarefrom a conventional sodium cyanide-process. Inaccordance with suchprocess and referring first to FIG. 1, wherein the path of the articlebeing plated is shownby the solid line A, the parts to be plated areplaced as customary within a perforated barrel or otherwise suit ablysupported and dipped in an alkaline cleaning solution contained in atank 10. Prior to this step the parts are suitably sandblasted, tumbled,or given other treatment as desired to remove burrs, flashings, etc., soas to provide a desired surface for plating. From the tank 10 the partsare passed to a rinse tank 12 where the parts are dipped, sprayed orotherwise suitably rinsed with water substantially to remove thealkaline cleaning solution which may be retained on the surface of theparts. Next the parts are dipped in an acid bath in a tank 14 to effectneutralization of any residual alkali which may remain on the parts.From the tank 14 the parts are carried to rinse tank 16 where the partsare again suitably rinsed with water.

From the tank 16 the parts are carried to and immersed in the platingsolution retained within one portion 18 of a dual chamber tank or cell20 illustrated in greater detail in FIG. 2. This may be the conventionalsodium cyanide solution. Referring to FIG. 2, the tank 20 is divided bya partition 22 of electrically non-conducting material so as to dividethe tank into two portions, the portion 18 which comprises a strikingbath and a further portion 24, comprising a drag out or pre-rinse baththe purpose for which will be described in detail subsequently. Thepartition 22 is provided with an opening 28 near the bottom of the tankso as to provide for fluid communication between the portions 18, 24whereby, as will be ssen, the ion concentration of the solution in thetwo portions will be substantially the same. The tank portion 18 isprovided wtih a brass anode or anodes 30 suspended on contact bars 32con nected to the positive side of a source of direct current electricalenergy. The plating barrel 34 within which the parts to be plated arecarried is shown suspended from a pair of cathode contacts 36 which areconnected to the negative side of the energy source. The striking stepis adapted to deposit a thin film of brass upon the parts.

When the desired strike plate has been made the parts are moved to aplating tank 40 provided with suitable brass anodes and conventionalmeans for applying plating current between the anodes and the parts inthe plating barrel 34.

After suitable plate is applied to the parts, the barrel 34 is liftedout of tank 40 and immersed in the portion 24 of the tank 20. Thissubstantially removes the concentrated plating solution from the platedparts. The barrel is then successively transferred through rinse tanks42, 44, 46 and 48 so as to effect rinsing of the parts and by the timethey are removed from tank 48, substantially complete removal of theplating solution from the surface of the parts is obtained. In each ofthese tanks the parts may be sprayed, tumbled or otherwise agitated toeffect rinsing of the surface thereof.

Attention is now directed to FIG. 3 constituting a flow chart of therecovery system of the invention. Since the solids recovery system isinvolved only with the plating tank 40 and subsequent rinses, theinitial wash and cleaning tanks 10 to 16, inclusive, are omit- 3 tedfrom FIG. 3. Indicated in FIG. 3 are the volumetric flow rates of atypical system and the dissolved solids concentrations at one point inthe cycle of operation. As the parts are moved from tank to tank theywill carry with them solution or so-called drag out. In the illustratedembodiment this amounts in volume to 0.75 liters per minute. Inaccordance with the invention, solution is continuously withdrawn fromthe third rinse tank 46 at a rate of 11.1 liters per minute and passedthrough a reverse osmosis cell 50, a suitable pump 52 being provided tomaintain sufficient pressure on the incoming fluid side of the cell tosecure reverse osmosis flow across the cell membrane which may be apolyamide type or other suitable type. The concentrate from cell 50 ispassed to the second rinse tank 44 at a rate of 15 3.7 liters perminute, the permeate to the fourth rinse tank 48 at a rate of 7.4 litersper minute. Tanks 46, 48 are interconnected to permit free flow betweenthem so that an unstricted counterflow of 7.4 liters per minute occursfrom tank 48 to tank 46.

46 at 3.7 liters per minute, the concentrate being returned at 7.4liters per minute to the holding tank 60. For reasons to be made clearthe cell 64 is operated only 50 percent of the time, all otheroperations running continuously. Provision is also made for adding makeup water to the fourth rinse tank as indicated at 66.

FIG. 3 shows system conditions at start up of a cycle. During thefollowing 12 hour period there will be no return of solution from theholding tank 60 to the plating tank 40. Instead, following start upsolution will be retained within the holding tank 60, graduallyincreasing in concentration as solution is cycled through the reverseosmosis cell 64. The approximate solids concentration in each tank atthe start of this cycle of operation is also shown in FIG. 3. The solidsconcentration is the total concentration of copper, zinc and sodiumcyanides and sodium carbonate.

The material balance in flow per minute in each tank at start up is asfollows:

First Rinse Tank 42 From tank 24, 0.75 1/min. X 100,000 ppm 75,000mg/min.

Out

To tank 46, 0.75 llmin. X 2150 ppm To tank 42,11.101/min. X 2150 ppm1,612 mg/min. 23,865 mg/min.

Total 25,447 mg/min. Third Rinse Tank 46 From tank 44, 0.75 1/min. X2150 ppm 1,612 mg/min. From cell 64, 3.70 I/min. X 1260 ppm 4,662mg/min. From tank 48, 7.40 l/min. X 212 ppm 1,568 mg/min. Total 7,842mg/min. Out

To tank 48, 0.75 l/min. X 1150 ppm 862 mg/min. To cell 50, 11.10 l/min.X 1150 ppm 12,765 mg/min. Total 13,627 mg/min. Fourth Rinse Tank 48 Fromtank 46, 0.75 l/min. X 1150 ppm 862 mg/min. From cell 50, 7.4 l/rnin. X115 ppm 851 mg/min. Total 1,713 mg/min. Out

With parts, 0.75 l/min. X 212 ppm 159 mg/min. To tank 46, 7.40 llmin. X212 ppm 1,568 mg/min. Total 1,727 mg/min.

Solution from the first rinse tank 42 is also continuously withdrawn ata rate of 1 1.1 liters per minute and passed through a pump 54 to secondreverse osmosis cell 56. The concentrate in this instance is passed to aholding tank 60 at a rate of 3.7 liters per minute, the permeate beingpassed at 7.4 liters per minute to the second rinse tank 44. Tanks 42,44 are interconnected so that an unrestricted counter flow of 1 1.1liters per minute occurs from tank 44 to tank 42.

To effect concentration of the solution in the holding tank 60 it iswithdrawn by a pump 62 at the rate of l 1.1 liters per minute and passedto a third reverse osmosis cell 64. The permeate is passed to the thirdrinse tank It will be observed that at this point in time the system isnot balanced. All of the tanks are being depleted, the third rinse tank46 undergoing the greatest rate of change. However, as the third reverseosmosis cell continues to operate concentrating the solution in theholding tank 60, it will feed a continuously enriching permeate to thethird rinse tank 46 eventually effecting a return sufficient to make upthe excess solids withdrawn during the initial period of the cycle. Theother tanks will likewise receive a balancing flow.

It will be appreciated that the concentrations in the various tanks willvary from time to time. For example. the plating solution of tank 40 mayvary from 150,000

ppm to z'sopoo' pni over a 'corriplete' cycle and'the solution in theother tanks will also vary' although to a lesser degree. 7 i I At theendof the 12' hour period of operation of the reverse osmosis cell 64, itsoperation-is terminated. Makeup water is then started-into rinse tank4.8 at 3.7 liters'per minute. At the same timethe solution in theholding tank 60 is returned to the plating tank 40 since in thepreceding period it has lost fluid by dragout loss andevaporation. Alsosince the electroplating operation is not one hundred percent efficient,it will be necessary to add make up copper cyanide, zinc cyanide andsodium cyanide to the plating tank 40 in amount sufficient to maintainthe desired concentrations therein. Some of the solution from theholding tank will also be returned to the tank to make up for solutionlost by evaporation.

As the reverse osmosis cells 50, 56, 64 lose efficiency, adjustmentswill have to be made in the flow rates through the various cells so asto maintain the system balance. For this purpose suitable flow controlvalves and flow rate meters (not shown) may be placed in the variouslines.

It will be observed that the concentration of the solution in tank 20 isonly one-half that in the plating tank 40. Thus, while serving as aconvenient strike tank it serves the equally important function ofreducing the concentration of dragout carried into the rinse tank 42 by50 percent. This reduces the metal ion and cyanide content in the rinsesolution of tank 42 by like amount and likewise reduces theconcentration in the subsequent tanks reducing by one-half the totalamount of chemicals to be treated in the reverse osmosis cells 50 and56. This reduction in ion concentration in the solution in first rinsetank 42 and third rinse tank 46 results in increased efficiency inoperation of the reverse osmosis cells 50, 56, since the osmoticpressure which has to be overcome will be reduced. Substantial savingsin power are thus realized.

The reverse osmosis cell 64 maintains an ion balance in third rinse tank46. As indicated above, without the feedback of product from cell 64,tank 46 would suffer a depletion in ion content and the entire systemwould become unbalanced if it were attempted to operate it continuously.Without the cell 64 the system may be operated for 16 hours out of 24,but plating operations must be discontinued for 8 hours out of a 24 hourperiod in order to permit sufficient evaporation from the plating tankto permit return from the holding tank of all of the permeate collectedfrom reverse osmosis cell 56. The reverse osmosis cell 64 reduces thevolume of the holding tank by about one-third enabling platingoperations to be carried out continuously.

The illustrated system utilizes four rinse tanks. However, if a higherdissolved content could be tolerated in the final rinse the fourth rinsetank 48 could be eliminated in which case the product from reverseosmosis cell 50 would be returned directly to tank 46 and make up wateralso added directly to such tank. Alternatively additional rinse tankscould be added and the product of cell 50 simply passed to the finalrinse tank.

As will be observed, the system illustrated is completely closed. Nochemicals are removed from the system except for the very minor amountcarried out on the parts from the fourth rinse tank 48. Thus, besideseliminating costly cyanide destruction and costly metal ion recoveryprocesses that otherwise would have to be employed, the system permitsmaximum utilization of 6 plating'metal and electrolytic bath chemicals.The system also conserves water, the only loss being evaporativeloss-and thatcarried out with the parts from the final rinse-tank.

The system described would also be adaptable inyany type of hot'p'latingprocess-wherein an evaporative loss occurs in the plating tank, forexample, copper, nickel or'chromium plating. In a cold system, such asis used in zinc plating, an evaporating arrangement would have to beemployed with the plating bath to remove sufficient water to enablereceipt of the holding tank solution.'Moreover, while the invention hasbeen described in connection with an electroplating process, it will beapparent it has usefulness in other types of plating processes.

Having illustrated and described a preferred embodiment of theinvention, modifications in arrangement and detail will be apparent tothose of ordinary skill in the art.

I claim:

1. In a plating process wherein articles are plated in a solution withina plating tank and thereafter rinsed in a series of at least three rinsetanks, the improvement comprising,

providing a dual chamber tank having an electrically non-conductingdivider therein separating the dual chamber tank into two portionsincluding a plating portion and a rinse portion, said divider having anopening therein to permit flow of solution between said one portion ofsaid dual chamber tank and the other portion thereof,

plating an article in said one portion of said dual chamber tank,

passing the article from said tank one portion to said plating tank andeffecting a plating on said article, passing the article from saidplating tank to the said other portion of said dual chamber tank,thereafter passing said article seriatum to said rinse tanks,continuously withdrawing solution from the first of said rinse tanks andsubjecting it to a first reverse osmosis while continuously passing theconcentrate from said first reverse osmosis to a holding tank and thepermeate to the second of said rinse tanks,

continuously withdrawing solution-from the third of said rinse tanks andsubjecting it to a second reverse osmosis while continuously passing theconcentrate from said second reverse osmosis to said second rinse tankand the permeate to the final one of said rinse tanks,

and returning solution from said holding tank to said plating tank.

2. The process of claim 1 wherein said solution is accumulated in saidholding tank for predetermined periods of time and periodically returnedto said plating tank. I

3. The process of claim 2 including periodically terminating saidplating and evaporating solvent from the plating solution prior to thereturn of solution from said holding tank.

4. The process of claim 1 comprising withdrawing the solution from saidholding tank and subjecting it to a third reverse osmosis while passingthe permeate to said third rinse tank and returning the concentrate tosaid holding tank.

5. The process of claim 3 wherein said solution in said holding tankperiodicallyjs subjected to said third reverse osmosis and at thetermination of said third 7 reverse osmosis cycle the solution in saidholding tank is returned to said plating tank.

6. The process of claim comprising adding make up solvent to said finalrinse tank as said solution is returned to said plating tank.

7. The process of claim 6 wherein said solution is a brass cyanideplating solution and said solvent is water.

8. In a plating process wherein articles are plated in a solution withina plating tank and thereafter rinsed in a series of rinse tanks, theimprovement comprising,

providing a dual chamber tank having an electrically non-conductingdivider therein separating the dual chamber tank into two portions,

8 said divider having an opening therein to permit flow of solutionbetween said one portion of said dual chamber tank and the other portionthereof, plating anarticle in said one portion of said dual chambertank, passing the article from said tank one portion to said platingtank and effecting a plating of said article, passing the article fromsaid plating tank to the said other portion of said dual chamber tank,and thereafter passing said article seriatum to said rinse tanks.

1. IN A PLATING PROCESS WHEREIN ARTICLES ARE PLATED IN A SOLUTION WITHINA PLATING TANK AND THEREAFTER RINSED IN A SERIES OF AT LEAST THREE RINSETANKS, THE IMPROVEMENT COMPRISING, PROVIDING A DUAL CHAMBER TANK HAVINGAN ELECTRICALLY NONCONDUCTING DIVIDER THEREIN SEPARATING THE DUALCHAMBER TANK INTO TWO PORTIONS INCLUDING A PLATING PORTION AND A RINSEPORTION, SAID DIVIDER HAVING AN OPENING THEREIN TO PERMIT FLOW OFSOLUTION BETWEEN SAID ONE PORTION OF SAID DUAL CHAMBER TANK AND THEOTHER PORTION THEREOF, PLATING AN ARTICLE IN SAID ONE PORTION OF SAIDDUAL CHAMBER TANK, PASSING THE ARTICLE FROM SAID TANK ONE PORTION TOSAID PLATING TANK AND EFFECTING A PLATING ON SAID ARTICLE, PASSING THEARTICLE FROM SAID PLATING TANK TO THE SAID OTHER PORTION OF SAID DUALCHAMBER TANK, THEREAFTER PASSING SAID ARTICLE SERIATUM TO SAID RINSETANKS, CONTINUOUSLY WITHDRAWING SOLUTION FROM THE FIRST OF SAID RINSETANKS AND SUBJECTING IT TO A FIRST REVERSE OSMOSIS WHILE CONTINUOUSLYPASSING THE CONCENTRATE FROM SAID FIRST REVERSE OSMOSIS TO A HOLDINGTANK AND THE PERMEATE TO THE SECOND OF SAID RINSE TANKS, CONTINUOUSLYWITHDRAWING SOLUTION FROM THE THIRD OF SAID RINSE TANKS AND SUBJECTINGIT TO A SECOND REVERSE OSMOSIS WHILE CONTINUOUSLY PASSING THECONCENTRATE FROM SAID SECOND REVERSE OSMOSIS TO SAID SECOND RINSE TANKAND THE PERMEATE TO THE FINAL ONE OF SAID RINSE TANKS, AND RETURNINGSOLUTION FROM SAID HOLDING TANK TO SAID PLATING TANK.
 2. The process ofclaim 1 wherein said solution is accumulated in said holding tank forpredetermined periods of time and periodically returned to said platingtank.
 3. The process of claim 2 including periodically terminating saidplating and evaporating solvent from the plating solution prior to thereturn of solution from said holding tank.
 4. The process of claim 1comprising withdrawing the solution from said holding tank andsubjecting it to a third reverse osmosis while passing the permeate tosaid third rinse tank and returning the concentrate to said holdingtank.
 5. The process of claim 3 wherein said solution in said holdingtank periodically is subjected to said third reverse osmosis and at thetermination of said third reverse osmosis cycle the solutioN in saidholding tank is returned to said plating tank.
 6. The process of claim 5comprising adding make up solvent to said final rinse tank as saidsolution is returned to said plating tank.
 7. The process of claim 6wherein said solution is a brass cyanide plating solution and saidsolvent is water.
 8. In a plating process wherein articles are plated ina solution within a plating tank and thereafter rinsed in a series ofrinse tanks, the improvement comprising, providing a dual chamber tankhaving an electrically non-conducting divider therein separating thedual chamber tank into two portions, said divider having an openingtherein to permit flow of solution between said one portion of said dualchamber tank and the other portion thereof, plating an article in saidone portion of said dual chamber tank, passing the article from saidtank one portion to said plating tank and effecting a plating of saidarticle, passing the article from said plating tank to the said otherportion of said dual chamber tank, and thereafter passing said articleseriatum to said rinse tanks.